For my Orcas, I used the AT 43 red block Kolossus models.
I thought they were to short and not really functional so I made and cast a resin mid section to add height to the model, now thw model can swival.
Because the model is higher (about a 1/4 inch higher) it does not look so stubby. Also poped the weapons off the model and re did them to look more like the Orca weapons and the price is right 3 for $10.00!
I will have to get some pictures up here.